1. Field of the Invention
The present invention relates to an insert earphone, particularly to a structure of an ear chip thereof.
2. Description of the Related Art
An insert earphone conventionally comprises a receiver unit having a sound passage tube, and an ear chip attached to the receiver unit. The insert earphone is used in state where the ear chip is inserted into an external auditory meatus.
The ear chip of the insert earphone comprises a barrel portion and an annular flange portion. The barrel portion defines a sound passage which communicates to a sound passage of the sound passage tube of the receiver unit. The annular flange portion has the shape of a parabola spreading from the top end of the barrel portion toward the base end thereof. When the ear chip is inserted into the external auditory meatus, the insert earphone is supported by the annular flange portion. The annular flange portion abuts on a wall face of the external auditory meatus to prevent a sound from leaking.
In order to produce a stable sound quality in this type of earphone, it is essential that the shape of the sound passage is maintained when the ear chip is inserted into the external auditory meatus. Therefore, the barrel portion of the ear chip is made relatively thick to obtain sufficient rigidity. The annular flange portion is brought into close contact with the wall face of the external auditory meatus only by the distortion of the annular flange portion.
The ear chip may have a dual structure for the annular flange portion. One annular flange portion has a supporting function of the insert earphone, the other annular flange portion has an contacting function with the wall face of the external auditory meatus.
An insert earphone of this type is shown in FIG. 4. An ear chip 114 of an insert earphone 110 comprises a barrel portion 114A, a first annular flange portion 114B and a second annular flange portion 114C. The first annular flange portion 114B has the shape of a parabola spreading from the top end of the barrel portion 114A toward the middle thereof. The second annular flange portion 114C has the shape of a parabola spreading from the middle portion of the barrel portion 114A toward the base end thereof. The first annular flange portion 114B having a smaller outer diameter compared with the second annular flange portion comes into close contact with the wall face 2a at a depth region of the external auditory meatus 2 where improved acoustic characteristics (sufficient sound pressure) is available. Since the second annular flange portion 114C comes into contact with the wall face 2a at an entrance region of the external auditory meatus 2, the user do not feel uncomfortable by the second annular flange portion 114C in fitting the insert earphone 110. The insert earphone 110 is supported by the second annular flange portion 114C.
Such conventional insert earphone with a dual flange structure, however, has a disadvantage in that every part of periphery of the first annular flange portion 114B unevenly contacts with the wall face 2a since the external auditory meatus 2 extends in not a simple cylindrical shape but a complex curved shape. Since the first annular flange portion 114B is thick at the inner circumference neighborhood 114Ba like in the insert earphone with a single flange structure, the inner circumference neighborhood 114Ba is hardly distorted. Therefore, only the outer circumference neighborhood 114Bb is distorted. It likely causes a lack of pressing force against the wall face 2a of the external auditory meatus 2 by the first annular flange portion 114B.
Therefore, the ear chip 114 does not come into close contact with the external auditory meatus 2, causing a sound leakage.
In case where the ear chip 114 is inserted farther depth region of the ear to make the ear chip 114 more closely contact with the wall face 2a, the ear chip 114 reaches a first curved portion 2b of the external auditory meatus and the top end of a sound passage 114a in the ear chip 114 is clogged by the first curved portion 2b. 
On the contrary, the wall face 2a of the external auditory meatus 2 is pressed partially strongly by the outer circumference neighborhood 114Bb of the first annular flange portion 114B, the user feel uncomfortable in wearing the ear chip for a long time.